1. Field of the Invention
The present invention relates to a calendar mechanism, and a timepiece having the same.
2. Description of the Related Art
Regarding a calendar mechanism, various techniques are known as techniques for forming a so-called auto calendar mechanism which per forme month feeding for a longer month (a month which has 31 days and which is also referred to as a long month in this specification) and for a shorter month (a month which has not more than 30 days and which is also referred to as a short month in this specification) in different manners.
In an auto calendar mechanism, from the month end (30th day) of a shorter month other than February to the first day of a longer month, date feeding is effected by extra one day as an additional date feeding to perform date feeding by two days; in this connection, various mechanisms have been proposed; in particular, there has been proposed provision of a data indicator driving wheel with a paw structure adapted to rotate a date indicator separately from a date feeding finger so that additional date feeding can be effected at the end of a shorter month (JP-A-2009-128119 (Patent Document 1)).
In the calendar mechanism according to Patent Document 1, to perform additional date feeding on the date indicator at the end of a short month, a rigid finger is provided so as to be capable of translation with respect to the rotation shaft of the date indicator driving wheel as a short month end feeding finger structure operated by a month cam, generating a translation operation by the month cam in a short month and causing it to be engaged with the month end feeding tooth of the date indicator at the month end through the translation.
However, in this case, positional control in the radial direction of the date indicator driving wheel is to be performed on the rigid finger, so that the rigid finger constituting the month end feeding finger structure is retained so as to be capable of translation in the radial direction of the date indicator driving wheel within, the range of the diameter of the date indicator driving wheel with respect to the rotation center of the date indicator driving wheel, and is caused to translate in the radial direction by the month cam in a short month, which means a request for a rather complicated structure and for high dimensional precision is inevitable for the space that can be occupied by the finger structure support structure and the month cam structure.
A technique is also known according to which the position of the engagement portion of the date feeding finger is changed so that, additional date feeding can be effected between the end of a shorter month and the start of a longer month (Japanese Patent No. 2651150 (Patent Document 2)).
However, in the calendar mechanism according to Patent Document 2; an elastic arm portion of the date feeding finger is usually forcibly deformed (on days other than shorter month ends) to feed solely one tooth a day, so that the roughness load (the load applied to the rotation of the train wheel) is structurally likely to increase, which is likely to involve energy loss.
Various proposals have been made regarding the provision of a date wheel rotating mechanism separately from the date feeding finger so that additional date feeding can be effected from the end of a shorter month to the start of a longer couth (See, for example, JP-A-2005-326420 (Patent Document 3)).
However, in the calendar mechanism, for example, of Patent Document 3, there is employed a planetary gear mechanism with a predetermined number of teeth so that a predetermined operation can be performed, which means it is rather difficult to avoid, a very complicated structure.